1. Field of the Invention
The present invention relates to a multilayered piezoelectric/electrostrictive device. More particularly, the present invention relates to a multilayered piezoelectric/electrostrictive device which includes a piezoelectric/electrostrictive portion having extremely excellent piezoelectric/electrostrictive characteristics. This device offers excellent vibration transfer characteristics between the substrate and the piezoelectric/electrostrictive portion, exhibits little variation in the piezoelectric/electrostrictive characteristics even within the portions of a single piezoelectric/electrostrictive portion, and also exhibits excellent durability.
2. Description of Related Art
A piezoelectric/electrostrictive device is known to be able to control micro-displacement on the order of submicrons. A piezoelectric/electrostrictive device is generally used which includes a piezoelectric/electrostrictive portion formed of a piezoelectric/electrostrictive ceramic composition and having an electrode portion to which voltage is applied are layered on a ceramic substrate. In recent years, a multilayered piezoelectric/electrostrictive device in which a number of piezoelectric/electrostrictive portions and electrodes are alternately layered on the substrate are also used, since the output can be increased at a low applied voltage. The multilayered piezoelectric/electrostrictive device is suitable for controlling micro-displacement and has excellent characteristics such as high electrical/mechanical conversion efficiency, high-speed response, high durability, and small power consumption. Thus, the multilayered piezoelectric/electrostrictive device is used in various applications such as a piezoelectric pressure sensor, a probe moving mechanism for a scanning tunneling microscope, a linear guide mechanism for an ultra-precision machining device, a hydraulic pressure control servo valve, a head for a VTR device, a pixel for forming a flat panel image display device, or a head for an ink-jet printer.
Various studies have been made on the piezoelectric/electrostrictive ceramic composition used for forming the piezoelectric/electrostrictive portion. For example, a Pb(Mg1/3Nb2/3)O3—PbTiO3—PbZrO3 three-component solid solution composition or a piezoelectric/electrostrictive ceramic composition obtained by replacing a part of Pb in the composition with Sr or La is disclosed in JP-A-44-17103 and JP-A-45-8145, for example. It was expected that one may obtain a piezoelectric/electrostrictive device having excellent piezoelectric/electrostrictive characteristics (piezoelectric constant, for example) by using this composition to produce a piezoelectric/electrostrictive portion itself, which is the most important element which determines the piezoelectric/electrostrictive characteristics of the piezoelectric/electrostrictive device.
However, in case of the conventional piezoelectric/electrostrictive device, the piezoelectric/electrostrictive device is manufactured by performing a heat treatment after forming a piezoelectric/electrostrictive ceramic formed of the piezoelectric/electrostrictive ceramic composition on the substrate. Thus, contraction and densification of the piezoelectric/electrostrictive ceramic composition during the heat treatment are hindered because the substrate hardly contracts. Accordingly, the density of the piezoelectric/electrostrictive portion is decreased. As a result, problems arise, such as a decrease in the bending displacement or the occurrence of dielectric breakdown in the low density area when voltage is applied to the piezoelectric/electrostrictive portion. These problems become striking in a multilayered piezoelectric/electrostrictive device, and improvement is strongly demanded.
In view of the above-described situation, JP-A-11-29357 proposed that the densification of a piezoelectric/electrostrictive portion is attained by mounting a piezoelectric/electrostrictive portion obtained by heating a piezoelectric/electrostrictive ceramic to the substrate when the piezoelectric/electrostrictive ceramic is formed of a piezoelectric/electrostrictive ceramic composition that has been heated in advance. In this case, it is necessary to use an inorganic or organic adhesive when the piezoelectric/electrostrictive portion is mounted to the substrate. The adhesive, however, hinders the vibration transfer between the substrate and the piezoelectric/electrostrictive portion, or the adhesive component can deteriorate the characteristics of the piezoelectric/electrostrictive portion or the substrate.
In the case where variations in the piezoelectric/electrostrictive characteristics occur between the piezoelectric/electrostrictive portions or between portions (center and end, for example) within a single piezoelectric/electrostrictive portion of the piezoelectric/electrostrictive device including such a piezoelectric/electrostrictive portion is provided in an electronic instrument such as a transmitter or a sensor, it is difficult to provide the desired characteristics, and excellent transmission or accurate sensing can be hardly attained. Moreover, a piezoelectric/electrostrictive device having variations in the piezoelectric/electrostrictive characteristics between portions within a single piezoelectric/electrostrictive portion may pose a problem relating to durability due to stress concentrations caused by variations in the bending displacement.
In order to solve the above-described problems, a piezoelectric device including a piezoelectric portion formed of a piezoelectric ceramic composition containing a specific Pb(Mg,Ni)1/3Nb2/3O3—PbZrO3—PbTiO3 three-component solid solution composition, in which a part of the Mg is replaced with Ni, as an essential component is disclosed in JP-A-2001-388315, for example. However, the piezoelectric device disclosed in JP-A-2001-388315 does not fully eliminate variations in the piezoelectric/electrostrictive characteristics between the piezoelectric/electrostrictive portions or between different portions (center and end, for example) of a single piezoelectric/electrostrictive portion. Moreover, further improvements in durability are strongly demanded.